Apple has started pushing out reminder notifications to inform macOS users that support for 32-bit apps will be stopped soon. All Mac users running macOS 10.13.4 High Sierra will see a one-time alert when they open a 32-bit app.
The date of terminating the support for 32-bit apps on macOS is not yet disclosed – even on the alert notifications users received.
Apple had warned developers about the change at Apple’s Worldwide Developers Conference (WWDC) 2017, where it noted that High Sierra would be the last version to support 32-bit apps “without compromise.”
Presently, the alert users receive says that the app is not optimised for a Mac, but the app will continue to work.
To check if an app is 32-bit or 64-bit, go to About This Mac in the Apple menu. Click on the System Report button. Here, from the system report, scroll down to Software, then select Applications. Once you select the individual application, you will see a field titled 64-bit (Intel). If it says Yes, it means the app is 64-bit and a No indicates 32-bit.
If you have any 32-bit apps, you should check with the software developer to see if a 64-bit version is available.